(a) Field of the Invention
The present invention relates to an improved photosensitive material for use in electrophotography which is prepared by forming an inorganic or organic photoconductive layer on a conductive support.
(b) Description of the Prior Art
Generally known electrophotographic sensitive materials are prepared by forming, by a coating process, a photoconductive layer comprising a dispersion obtained by dispersing an inorganic or organic photoconductor such as zinc oxide, titanium oxide, anthracene, carbazole, etc. in a resin. In order to form an image on such a photosensitive material, there is usually employed the method of repeating the five steps of charging the photoconductive layer with electricity, exposing, developing with a dry or wet developer, transferring the developed image to a plain paper, and cleaning off the developer left on the photoconductive layer. However, repeated use of such a photosensitive material has been attended with such drawbacks as gradual abrasion, breakdown or exfoliation of the photoconductive layer surface. Increase of the ratio of the resin content in the photoconductive layer is admittedly effective for overcoming such drawbacks, but as it entails deterioration of the light sensitivity, it has been inevitable to compromise on a fixed mixing ratio, and accordingly, it has been difficult to obtain a photosensitive material that will meet both requirements of light sensitivity and durability simultaneously. Besides, there are frequent occasions when it becomes necessary to apply heat for the purpose of drying or curing the photoconductive layer at the time of preparing photosensitive materials. In such a case, because there is a fear of causing thermal degradation of the photoconductive layer and/or the support, it has been impossible to apply a sufficient heating, entailing frequent deterioration of the strength of the photoconductive layer. Further, in the case of developing with a wet-developer, the photoconductive layer surface is required to have resistance to the solvent, but inasmuch as photosensitive materials of this kind have been poor in resistance to solvents, they have been defective in that they show a remarkable deterioration of properties at the time of wet development.
Meanwhile, as an attempt to improve mainly the sensitivity of a photosensitive material comprising a single photoconductive layer as above, there is known a photosensitive material sensitized by lamination or prepared by forming two kinds of photoconductive layers different in properties one upon the other and disposed on a support, such as, one prepared by forming a layer of an inorganic or organic photoconductor resin dispersion and a layer of an organic photoconductor, in that order, on a support or one prepared by forming said two layers by reversing that order on a support. However, in the case of the photosensitive material wherein the layer of the dispersion constitutes the uppermost layer, it has been inferior in durability such as resistance to abrasion and solvents like in the case of the aforesaid single-layer type photosensitive material, while in the case of the photosensitive material wherein the layer of organic photoconductor constitutes the uppermost layer, it also has been insufficient in durability because of the insufficient physical strength of the layer of the dispersion constituting the lower layer.